As an embodiment of the American Dream, going from slavery to the chief executive's chair at Merrill Lynch in two generations is hard to match.

For Stan O'Neal, who is expected be forced out of Merrill later today, the journey began in the town of Roanoke, Alabama, in 1951. He reached the top of the investment banking world half a century later, via General Motors and Harvard – where, he later acknowledged, "not a lot of people looked like me".

The O'Neal family were no strangers to segregation and its after-effects. E. Stanley O'Neal was only born in Roanoke, 13 miles from his parents' home in the nearby community of Wedowee, because the local hospital would not serve African American patients.

O'Neal spent his early childhood delivering newspapers, picking corn and cotton on the family farm in Wedowee, and being educated in a one-room school built by his grandfather – a former slave.

This may seem remarkable, given that slavery was abolished in the US in 1865, and indeed some disbelieving fact-checkers have reportedly demanded to see proof.

According to O'Neal, he was around five years old when his 95-year-old grandfather died, indicating his grandfather was born in 1861 - before Lincoln's Emancipation Proclamation of 1862 and the ratification of the 13th Amendment - which abolished slavery - in most states three years later.

The grandson's steep ascent began when his father landed a job at General Motors in Atlanta, Georgia. This gave young Stan access to a better education, followed by a spot on the assembly line, and eventually a place studying engineering and industrial administration at the General Motors Institute.

From there, O'Neal secured a scholarship at Harvard, where he attained an MBA.

"I really didn't have an understanding of the world or any role models, but I had a strong desire to learn, and I think that is what pulled me through," he commented later.

After another eight years at the carmaker he crossed to Merrill Lynch in 1986 to run its high-yield business. There he excelled and was rapidly promoted, becoming CFO in 1998, president of the retail private client arm in 2000, and chief executive in 2002.

He later told Newsweek that he doubted he could have enjoyed such success in another country.

"It's maybe the only country in the world that could have somebody like me start out where I did and wind up doing what I'm doing," he said, adding that he had also been born at the right time.

"If I had been born 30 years earlier, there's no way that we'd ever be sitting here having this conversation."

As chief executive, O'Neal shook Merrill up. He cut around 24,000 jobs and axed several senior executives. Expensive corporate perks, including the gourmet meals that had been prepared for the board, were also ditched.

His actions proved unpopular with some staff, but the results were impressive – by 2003 Merrill was the most profitable investment bank on Wall Street, bringing in more money per broker than any rival.

In some quarters, the knives are out too. The Wall Street Journal dubbed O'Neal "famously aloof", while the New York Times claimed he was a loner who made few friends at Merrill during his 20 years there.